Cellular localization and functional role of phosphatidylcholine-specific phospholipase C in NK cells

Although several classes of phospholipases have been implicated in NK cell- mediated cytotoxicity, no evidence has been reported to date on involvement of phosphatidylcholine-specific phospholipase C (PC-PLC) in NK activation by lymphokines and/or in lytic granule exocytosis. This study demonstrated the expression of two PC-PLC isoforms (M-r 40 and 66 kDa) and their IL-2-de pendent distribution between cytoplasm and ectoplasmic membrane surface in human NK cells. Following cell activation by IL-2, cytoplasmic PC-PLC trans located from the microtubule-organizing center toward cell periphery, essen tially by kinesin-supported transport along microtubules, while PC-PLC expo sed on the outer cell surface increased 2-fold. Preincubation of NK cells w ith a PC-PLC inhibitor, tricyclodecan-9-yl-xanthogenate, strongly reduced N K-mediated cytotoxicity. In IL-2-activated cells, this loss of cytotoxicity was associated with a decrease of PC-PLC exposed on the cell surface, and accumulation of cytoplasmic PC-PLC in the Golgi region. Massive colocalizat ion of PC-PLC-rich particles with perforin-containing granules was found in the cytoplasm of NK-activated (but not NK-resting) cells; both organelles clustered at the intercellular contact region of effector-target cell conju gates. These newly detected mechanisms of PC-PLC translocation and function support an essential role of this enzyme in regulated granule exocytosis a nd NK-mediated cytotoxicity.